There is a great need for devices or apparatuses which make it possible to identify or detect objects in a contactless manner and over a certain distance. An additional desire exists to be able to change the data stored in, or operating characteristics of, such devices or apparatuses (i.e. "program" the devices or apparatuses).
It is, for example, desirable to request contactless and over a certain distance identifications which are uniquely assigned to an object and which are stored in the device or apparatus so that, for example, the object may be identified. A determination may also be made as to whether or not a particular object exists within a given reading range. This concept can be used in a number of applications including security identification (e.g., security badges), inventory control, waste management, vehicle identification, and many others.
One such identification system is disclosed in U.S. Pat. No. 5,053,774 ('774) issued on Oct. 1, 1991 to Schuermann et al. In that arrangement, the transponder (or responder) unit includes an energy accumulator which stores the energy contained in an RF interrogation pulse, which is transmitted from a reader (or interrogator). The transponder includes circuitry which senses the termination of the reception of the RF interrogation pulse and the presence of a predetermined energy amount in the energy accumulator. The circuitry triggers the excitation of an RF carrier wave generator operating with the frequency contained in the RF interrogation pulse. A signal generated by the RF carrier wave generator can then be retransmitted back to the reader thereby conveying information stored within the transponder.
In some applications the reading repetition rate of a transponder will be slow and it is desirable couple a number of reading antennas to a single RF reader module. Therefore, there is presently a need for an identification reader with multiplexed antennas.